Various arrangements and methods of fault diagnosis are known. The publication "Elektronik", issue 25/26 of 1981, in an article by Lawrenz and Timmermann, pp. 89-92, describes a method for error diagnosis of industrial control sequencing which is specifically adapted to decrease down time of machine tools upon malfunction of an electronic control system therefor. The error diagnosis, as described in this article, utilizes an error diagnostic program which tests or checks the input signals and output signals controlling the particular industrial process or sequencing with respect to error or malfunction. The example which is given in this article describes control of sorting of goods carried on a conveyor belt in which defective goods, for example some which do not have a label attached thereto or the like, are ejected from the normal production line for rework or the like. As described, malfunction in a system can arise due to defects not only in the control system as such, but also in transducers, cabling interconnecting the transducer, or transducers, and the actual control apparatus, in relays and wiring connected thereto, and the like. To detect errors, an error diagnostic program is provided which actually checks the input and output signals. A diagnostic calculator or computer arrangement is provided which is connected to the control elements, and input/output units over data buses. The diagnostic computer apparatus includes an error checking table, which is applied thereto by the user, in accordance with the desired operating program of the machine, in the selected example, the determination and ejection of incorrectly labeled or manufactured goods. The error checking table must contain the respective signal combinations, to be derived from and issued by the control apparatus, and which lists all the possible combinations of permitted and erroneous combinations of input and output signals, respectively.
Diagnosis of malfunction in accordance with the described method is complex. It requires, first, generation of the program which controls the industrial process, that is, the stored program relating input and output signals of the particular apparatus or machine which is to be controlled; this program, thus, must contain a table or memory addresses in which all commanded and permitted signal combinations are contained. For error diagnosis, then, it is additionally necessary to provide a further table which contains all possible signal combinations which are not permitted, or are indicative of malfunction. It is practically impossible to determine all possible combinations of error signals.
If the basic program is to be changed, even only slightly, it will then become necessary to correct the error checking table. Only those errors will be recognized which are contained within the error checking table.
The method, as described, thus is time-consuming and not unambiguously suitable for determining all possible errors since those which cannot be foreseen, of course, cannot be included within the diagnostic error table.